Ultrasonic waves have a vibration frequency higher than 20,000 Hz in which sounds of the vibration are not recognizable by human ears. Ultrasonic waves have a variety of applications, one of which is ultrasonic skin cleaning for cosmetic or other purposes. An example of an ultrasonic wave cosmetic device in the conventional technology is shown in Japanese Utility Model Registration No. 3015061. In this conventional example, a metallic probe head is provided with an ultrasonic wave vibration element on a surface opposite to a probe head metal surface which directly contacts the skin.
In the conventional ultrasonic wave cosmetic device noted above, the temperature of the ultrasonic wave vibration element as well as the probe head metal surface that contacts the skin (skin contact metal surface) may increase to a level which is too high for human skin. Such an increase in the temperature occurs when the ultrasonic wave vibration element is continuously driven for a long period of time or the ultrasonic wave is concentrated on a fixed point of the skin for a relatively long time. Therefore, one problem with conventional cosmetic devices of this kind is that they may burn or otherwise adversely affect the skin.